The present invention relates in general to a method and an apparatus for reconstituting or reconfiguring a ring network including a plurality of transmission nodes for allowing communication between terminals connected thereto. More particularly, the present invention is concerned with a network reconfiguring method and an apparatus which are suited for detecting a faulty location where the transmission apparatuses are by-passed by optical switches or the like means, involving section or interval loss greater than a predetermined level that may cause the operation of the ring network to be unstable, and/or for disconnecting the faulty location from the system or reconnecting it to the system after the fault is recovered.
A method for reconstituting or reconfiguring a transmission path reconstituting for a ring network data transmission system, is disclosed in an article entitled "A 100 Mb/s Optical Local Ring Network which interconnects plural Bus Networks" contained in a Japanese literature "Nikkel Electronics" Dec. 5, 1983, pp. 173-199. According to this known method, occurrence of transmission fault or failure is detected by a master station, which then issues a command signal commanding a search for the faulty location to the other stations, whereupon each station as well as the master station, checks whether the adjacent station the faulty station, which is then followed by issuance of a command to the faulty adjacent station as detected for transition to a loopback state. However, in the case of this known system, no consideration is made to the disconnection of an unstable location brought about by bypassing a multiplicity of successive stages of the transmission apparatuses, not to speak of the much complicated structure of the detecting means for detecting the unstable state and the amount of time required for the reconstitution (reconfiguration) of the network system.
Further, there is disclosed in Japanese Patent Application Laid-Open No. 137154/1985 (JP-A-60-137154) a transmission path reconstituting method for dealing with the unstable transmission state brought about by signal loss of a magnitude greater than a permissible value in a section where a number of successive transmission stations (apparatuses) are bypassed, i.e. the unstable state in which the transmission error rate is increased beyond a prescribed value or varies significantly in dependence on changes in the environmental conditions. In the case of this known system, however, the message, for example, the power-down of the power of a transmission apparatus is given to the adjacent apparatus through a line provided additionally only for this purpose. Consequently, overall system cost is undesirably increased due to the necessity of providing the abovementioned message line in addition to the inherent transmission lines, giving rise to a problem.